CVE-2025-26665 is a high-severity vulnerability identified in Microsoft Windows 10 Version 1809, specifically affecting the upnphost.dll component. The vulnerability is categorized under CWE-591, which relates to sensitive data storage in improperly locked memory. This means that sensitive information is stored in memory regions that are not adequately protected against unauthorized access. An authorized local attacker with limited privileges can exploit this flaw to elevate their privileges on the affected system. The vulnerability arises because the upnphost.dll module fails to lock memory properly, allowing sensitive data to be exposed or manipulated. Exploitation does not require user interaction but does require local access with some privileges (PR:L). The attack complexity is high (AC:H), indicating that exploitation may require specific conditions or expertise. The vulnerability impacts confidentiality, integrity, and availability, as indicated by the CVSS vector (C:H/I:H/A:H). No known exploits are currently reported in the wild, and no patches have been linked yet, suggesting that mitigation may rely on workarounds or system hardening until official updates are released. The vulnerability was published on April 8, 2025, with a CVSS v3.1 score of 7.0, reflecting its significant risk level.

For European organizations, this vulnerability poses a substantial risk, especially in environments where Windows 10 Version 1809 is still in use. The ability for a local attacker to escalate privileges can lead to unauthorized access to sensitive data, disruption of services, and potential lateral movement within networks. This is particularly critical for sectors handling sensitive personal data under GDPR, such as healthcare, finance, and government institutions. The exposure of sensitive data in memory can lead to data breaches, regulatory penalties, and reputational damage. Additionally, the integrity and availability impacts could disrupt business operations, especially if attackers leverage elevated privileges to deploy ransomware or other malicious payloads. Organizations relying on legacy systems or with insufficient patch management processes are at higher risk. Since exploitation requires local access, insider threats or compromised endpoints are the most likely attack vectors.

1. Immediate mitigation should focus on restricting local access to systems running Windows 10 Version 1809, ensuring only trusted users have login capabilities. 2. Implement strict endpoint security controls, including application whitelisting and behavior monitoring, to detect and prevent unauthorized privilege escalation attempts. 3. Employ memory protection tools or third-party solutions that can detect or prevent improper memory handling. 4. Conduct thorough audits of systems to identify any instances of Windows 10 Version 1809 still in operation and prioritize their upgrade to supported, patched versions of Windows. 5. Apply principle of least privilege rigorously to limit the impact of any local compromise. 6. Monitor system logs and security alerts for unusual local privilege escalation activities. 7. Once Microsoft releases an official patch, prioritize its deployment across all affected systems. 8. Educate users and administrators about the risks of local privilege escalation and enforce strong physical and network access controls to reduce insider threat risks.